Modular curvilinear staircase

ABSTRACT

Provided is a curved staircase installed between upper and lower levels of a building structure. The curved staircase may be configured as an “outside radius free-standing” version, an “inside radius free-stranding” version, or as an “entirely free-standing” version using a plurality of step modules disposed in stacked relationship to one another. The step modules may be configured in single-step and/or dual-step versions. Each one of the step modules has at least one side panel and at least one riser assembly which comprises a tread ledger and a front riser. A tread is mounted on the tread ledger and side panel of each of the step modules. Each of the treads is also supported by the front riser of the immediately lower adjacent one of the step modules. Inner and outer reinforcing panels are disposed in overlapping relationship to the side panel to interconnect the step modules.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part application of pending U.S. patent application Ser. No. 11/189,580 entitled MODULAR CURVILINEAR STAIRCASE and filed on Jul. 26, 2005, the entire contents of which is expressly incorporated by reference herein.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT (Not Applicable) BACKGROUND OF THE INVENTION

The present invention relates generally to building construction and, more particularly, to a uniquely configured curved staircase that is constructed of individual-step modules that are pre-manufactured off-site and which are then assembled in stacked arrangement at a job site and inter-connected to a building structure.

In building construction and, more particularly, in home construction, the installation of a curved stairway adds to the aesthetic appeal of a home interior. Furthermore, homeowners and builders realize that a curved staircase is generally a good investment in that a curved staircase may increase the home's resale value compared to the relatively lesser value added by a simple, straight staircase. Unfortunately, prior art curved staircases are generally more expensive than straight staircases. Such increased expense is due in large part to the cost of forming the curved portions of the curved staircase. Furthermore, the installation of a curved staircase requires a higher degree of skill and is sometimes comparable to the high level of skill required in cabinet making.

The increased expense is also due in part to the time consuming manner in which such curved staircases are installed. For example, prior art methods of curved staircase construction include trial-and-error cutting and fitting of the staircase framing as well as fitting of the individual components of the staircase. Prior art building methods are also typically performed entirely at the job site wherein the curved staircase is built into the structure.

In such methods, an outer wall is framed with studs and an inner wall is then framed with the stringers being attached to the studs of the inner wall. Risers are then cut and assembled into individual-steps to tie the outer wall to the inner wall in order to form the curved staircase steps. As may be appreciated, such conventional method for curved staircase construction is extremely time-consuming. Furthermore, such conventional building method is highly dependent upon skilled labor and the availability of specialized tooling in order to produce a staircase that meets precise tolerance requirements mandated by local and national building codes.

In an attempt to reduce the time and cost required to construct curved staircases, several manufacturers have developed pre-assembled completed curved staircases that are assembled at a factory and shipped as a unit to the job site. Such pre-assembled staircases are then installed by interconnecting the staircase at strategic points to the building structure. Unfortunately, due to the difficulty in controlling the tolerances of the building structure to which the completed staircase is to be connected, problems with fitment of the curved staircase may occur. In addition, generation of excess material wastage, schedule conflicts such as with framers, and issues in meeting building code requirements may develop.

Furthermore, the shipping of an entire completed curved staircase to a building structure many miles from the factory may entail significant logistical problems and may incur great expense. In addition, the cost of pre-manufacturing such a curved staircase may run into the many thousands of dollars even prior to final installation into a building structure. Finally, such prior art building construction of curved staircases may result in problems with the structural integrity of the curved staircase and, more particular, problems associated with the connection of the curved staircase to upper and lower levels of the building structure. A common problem that may develop with curved staircases of the prior art is that staircase squeakage may occur over time due to gradual loosening of joints in the staircase.

As can be seen, there exists a need in the art for a curved staircase that can be constructed within various building code limits. Furthermore, there exists a need in the art for a curved staircase that can be pre-manufactured in modular form and shipped as individual components to a job site. Additionally, there exists a need in the art for a curved staircase that can be manufactured to precise tolerances using specialized machinery in climate-controlled conditions of a pre-manufacturing facility. Also, there exists a need in the art for a curved staircase that can be initially designed to be compatible with the building structure using computer aided design techniques in order to avoid costly errors during final installation. Finally, there exists a need in the art for a curved staircase that is of low cost and that can be easily installed in a drastically reduced amount of time.

BRIEF SUMMARY OF THE INVENTION

The present invention specifically addresses the above referenced needs associated with curved staircases. More specifically, the present invention is a uniquely configured step module that may be arranged to form a staircase that is constructed of a stack of individual step modules. The step modules may be configured to produce a straight staircase, a curved staircase, or any combination thereof. The step modules may be prefabricated or pre-manufactured such as at an offsite location and which are then assembled in stacked arrangement at a job site. Advantageously, the step modules of the present invention may be manufactured using unskilled labor and with precision tooling and machinery in order to reduce costs and assembly time.

The staircase comprises a plurality of the step modules, a plurality of treads mounted on the step modules and a plurality of inner and outer reinforcing panels disposed in overlapping relationship to the side panels of the step modules. Although the step module may be used to form either the curved, straight, or combination staircase, for purposes of the following discussion, a curved staircase will be the subject of the disclosure. The curved staircase extends between upper and lower levels of a building structure. The step modules may be configured to produce the curved staircase as an entirely free-standing staircase that is configured to connect to upper and lower levels of the building structure. Alternatively, the step modules may be configured to produce the curved staircase as an inside radius free-standing staircase wherein only the inner radius of the staircase is free-standing and unsupported while the outer radius of the curved staircase is interconnected to the building structure.

More specifically, for the inside radius free-standing version, the outer radius of the curved staircase is interconnected to framing comprised of vertically oriented wall studs that extend between the upper and lower levels of the building structure. Additionally, it is contemplated that the curved staircase may be an outside radius free-standing staircase wherein only the outer radius of the staircase is free-standing and unsupported while the inner radius of the curved staircase in interconnected to the building structure. More specifically, for the outside radius free-standing version, the inner radius of the curved staircase is interconnected to framing of the building structure.

Regardless of whether the curved staircase is configured as the entirely free-standing version, the inside radius free-standing version, or the outside radius free-standing version, each one of the step modules may be preassembled and pre-manufactured such as by using specialized tooling. Each one of the step modules is comprised of at least one side panel for the inside and outside radius free-standing version. Alternatively, each one of the step modules is comprised of a pair of side panels that are disposed in spaced relation to one another for the entirely free-standing version of the curved staircase. In addition, each one of the step modules includes at least one riser assembly comprised of a front riser abutted up against a back riser, the back riser being referred to herein as a tread ledger

The side panel(s) may be straight or generally arcuately shaped (i.e., curved) or any combination thereof and may have an outer convex surface and an inner concave surface. The arcuate shape of the side panel is achieved by fabricating a plurality of laminated members in layered relationship to one another. The laminated members may be formed in a straight or curved shape and may be formed of bonded particulate material fabricated from cellular fiber, shredded paper, wooden particles, sawdust and various combinations thereof. The particulate material of the laminated members may be interconnected using a matrix resin. Under sufficient temperature and pressure, the side panel may be formed with a desired shape such as at a radius of curvature for the curved staircase.

For the entirely free-standing version as well as for either the outside radius or inside radius free-standing versions, the step modules may be configured as a single step version of the step module or in a dual step version. The single step version of the step module includes a single one of the riser assemblies. The dual step version of the step module includes a pair of the riser assemblies. The dual step version of the step module may also include the pair of riser assemblies extending laterally outwardly from the side panel and being connectable to the wall studs.

The pair of riser assemblies are preferably disposed in staggered relationship to one another. Each one of the riser assemblies comprises a tread ledger and a front riser which extends upwardly past the tread ledger. The front riser is preferably disposed in abutting contact to the tread ledger. For the single step version of the step module, each one of the side panels is constructed at a riser height which is generally equivalent to a height of the tread ledger. For the dual step version of a step module, the side panel(s) has a main portion with a front extension protruding outwardly therefrom.

For the dual step version of the step module, the front extension of the side panel is formed at the riser height while the main portion of the side panel is formed at twice the riser height. The tread ledger of the forward riser assembly has an upper edge that is generally flush with the front extension upper edge. The front riser of the forward riser assembly has an upper edge that is generally flush with the main portion upper edge. The tread ledger of the aft riser assembly has an upper edge that is generally flush with the main portion upper edge. The riser of the aft riser assembly has an upper edge that extends upwardly past the main portion upper edge to a level equal to that of the riser height.

As was earlier mentioned, the curved staircase includes a plurality of the treads. Each one of the treads is supported by the side panels for the free-standing version of the curved staircase. For the inside radius free-standing curved staircase, each one of the treads is supported by the side panel on the inner radius side of the curved staircase. The tread ledger forms the aft mounting surface for the tread while the front riser forms the forward mounting surface for the tread. As was earlier mentioned, upper edges of the side panel(s) and the tread ledger are preferably flush with one another such that the tread may be evenly supported thereupon.

The front riser is also preferably flush with the side panel upper edges and the tread ledger upper edge. For the dual step version of the step module, the front riser may be a component of the immediately lower adjacent one of the step modules or it may be a component of the same one of the step modules of which the tread ledger is a component. The front riser determines the height of each one of the steps of the curved staircase. The side panel and tread ledger are formed at the riser height.

Each of the step modules is preferably disposed in stacked relationship to one another and are also angularly spaced relative to one another. For either the inside or outside radius free-standing versions of the curved staircase, the angular orientation and spacing between adjacent ones of the step modules is preferable equivalent to the spacing between the wall studs of the building structure to facilitate interconnection of the step modules thereto. For the entirely free-standing version of the curved staircase, the angular spacing between the step modules is complementary to the width of the treads. The step modules are angularly spaced in order to create a suitable width for the tread mounting. Each one of the treads is preferably mounted so as to be abutted up against the front riser of the step module upon which the tread is mounted.

Regardless of whether the curved staircase is fabricated using the single step version or the dual step version of the step module (or any combination thereof) and regardless of whether the curved staircase is constructed as either the inside radius or outside radius free-standing versions or as the entirely free-standing version (which lacks any intermediate support of a wall), the step modules, and more particularly, the side panels may have non concentric radii of curvature. In this regard, such curved staircase having different radii of curvature for the inner and outer side panels may incorporate a flare in the width of the staircase in a direction from the upper level to the lower level. Furthermore, it is contemplated that the curved staircase may include straight sections that taper into curved sections. Regardless of the shape of the curved staircase, the step modules are appropriately shaped and are prefabricated as laminated side panels.

Manufacturing grade plywood may be utilized for fabricating the front riser and tread ledger. The treads may be fabricated of any material that is suitably hard. In this regard, exemplary materials for the tread include, but are not limited to, manufacturing grade plywood or any hard wood such as oak, mahogany, cherry and birch. Following the stacking and angular orientation of the individual ones of the step modules, a plurality of inner reinforcing panels is then disposed in overlapping relationship to the inner concave surfaces of the side panels. Preferably, each one of the inner reinforcing panels overlaps at least one of the module joints in order to interconnect adjacent ones of the modules. Preferably, the inner reinforcing panels abut against one another in order to form a plurality of inner panel joints that are likewise horizontally oriented and are staggered in relationship to the module joints.

A plurality of outer reinforcing panels may be disposed in overlapping relationship to the inner reinforcing panels and preferably extend across the inner panel joints. Each one of the outer reinforcing panels preferably straddles at least one of the inner panel joints. The outer reinforcing panels form a plurality of outer panel joints that are disposed in staggered relationship to the inner panel joints. Both the inner and outer reinforcing panels are preferably fabricated as pre-manufactured laminated units having the appropriate radius of curvatures incorporated thereinto. The curved staircase may include at least one strap member located at the upper and lower levels to interconnect the curved staircase to the building structure.

The laminated members making up the inner and outer reinforcing panels may be comprised of bonded particulate material to facilitate forming of the appropriate radius of curvature. Due to its flexible characteristics, bonded particulate material is preferably formed in the same manner as that for forming the side panels. The inner and outer reinforcing panels are preferably cut to an appropriate height to overlap at least one of the module joints and inner panel joints, respectively. The inner and outer reinforcing panels are disposed in abutting edge to edge contact with one another when overlaid on the side panels.

BRIEF DESCRIPTION OF THE DRAWINGS

These as well as other features of the present invention will become more apparent upon reference to the drawings wherein:

FIG. 1 is a perspective view of a curved staircase in an inside radius free-standing version thereof and which illustrates a plurality of step modules that may be assembled in stacked angular spaced configuration and which may be interconnected to wall studs of a building structure;

FIG. 2 is a perspective view of one of the step modules in a single step version thereof which may be utilized in an inside radius free-standing version of the curved staircase and illustrating the step module comprising a side panel, a front riser and a tread ledger extending laterally outwardly therefrom;

FIG. 2 a is a perspective view of the single step version of one of the step modules which may be utilized in an outside radius free-standing version of the curved staircase;

FIG. 2 b is a perspective view of one of the step modules in a single step version thereof which may be utilized in an entirely free-standing version of the curved staircase;

FIG. 3 a is a perspective view of the curved staircase in the inside radius free-standing version and which utilizes the single step version of the step module and which illustrates the stacking of the step modules to form a plurality of module joints therebetween;

FIG. 3 b is a perspective view of the curved staircase shown in FIG. 3 a and illustrating a front riser of the step module being interconnected to wall studs of the building structure;

FIG. 4 is a perspective view of the curved staircase of FIG. 3 a and illustrating a strap member interconnecting the curved staircase to an upper level of the building structure;

FIG. 5 is a perspective view of one of the step modules in a dual step version thereof and which may be utilized for the entirely free-standing version of the curved staircase and illustrating a spaced pair of the side panels having a pair of riser assemblies extending therebetween with each of the riser assemblies comprising a front riser disposed in abutting contact to a tread ledger; and

FIG. 6 is a perspective view of the curved staircase in the entirely free-standing version and which utilizes a plurality of the dual step versions of the step modules assembled in stacked, angularly spaced arrangement.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein the showings are for purposes of illustrating the present invention and not for purposes of limiting the same, shown in FIGS. 1-6 is a staircase 10 of the present invention which is constructed of pre-manufactured step modules 36 and which may be configured to form a straight or a curved staircase 10 or any combination thereof. However, for purposes of this discussion, the staircase will be described with reference to a curved staircase 10.

As can be seen in FIGS. 1 and 6, the step modules 36 may be assembled in stacked arrangement on top of one another. The staircase 10 may be provided in an “entirely free-standing” 74 version wherein the curved staircase 10 is not connected to the building structure 12 at any intermediate points between upper and lower levels 14, 16 of the building structure 12.

In this regard, the entirely free-standing version 74 of the staircase 10 bears its own weight and provides its own stability without any structural support from the walls of the building structure 12. The curved staircase 10 of the present invention may also be configured as an “inside radius free-standing” version 72 wherein an inside radius thereof is self-supported (i.e., is unsupported by a wall) while an outside radius of the curved staircase 10 is interconnected to the building structure 12 (i.e., is supported by a wall). Additionally, the curved staircase 10 of the present invention may also be configured as an “outside radius free-standing” version (not shown) wherein only an outer radius thereof is free-standing while the inner radius of the curved staircase is interconnected to the building structure 12.

Although the disclosure herein relates to an “outside radius free-standing” version, an “inside radius free-stranding” version 72, and an “entirely free-standing” version 74, it is contemplated that the curved staircase 10 may be adapted for use as a fully supported staircase wherein weight-bearing walls support both sides (i.e., inner and outer radii) of the curved staircase 10. Such weight bearing walls may be used to enclose a closet, a half-bath or a basement stairwell which may be disposed beneath the curved staircase 10.

As was earlier mentioned, the curved staircase 10 of the present invention is fabricated of pre-formed or pre-manufactured step modules 36 which may be fabricated using unskilled labor with precision tooling and machinery in a climate-controlled facility. Under such controlled conditions, the resulting step modules 36 may be produced with tight manufacturing tolerances. Advantageously, the individual step modules 36 may be shipped to the job site at a reduced cost as compared to the cost of shipping an entire staircase 10 to a job site. In addition, the step modules 36 may be assembled in a fraction of the time that is required to build a conventional curved staircase 10 into a building structure 12 at a job site.

In its broadest sense, the curved staircase 10 comprises a plurality of step modules 36, a plurality of treads 54 mounted upon the step modules 36, and a plurality of inner and outer reinforcing panels 58, 62 which are disposed in overlapping relationship to one another for interconnection of the step modules 36. As can be seen by reference to the figures, the curved staircase 10 may extend between upper and lower levels 16, 14 of the building structure 12. The building structure 12 may include framing 24 comprised of a plurality of spaced, vertically oriented wall studs 26 that extend at least between the upper and lower levels 16, 14 of the building structure 12. Additionally, blocking 28 may be locally attached to certain areas of the wall studs 26 to facilitate attachment of the front risers 46 for the inside radius free-standing version 72 of the curved staircase 10.

For the inside radius free-standing version 72, the step module 76 may be constructed similar to that shown in FIG. 2 wherein the front riser 46 is specifically adapted to be interconnected to the vertical wall studs 26, either directly or indirectly, so as to provide a load bearing path for an outer radius side of the curved staircase 10. For such versions, the inner radius side is generally free-standing and is supported only at the upper and lower levels 16, 14 of the building structure 12. For the outside radius free-standing version of the curved staircase 10, the step module 76 may be constructed similar to that shown in FIG. 2 a wherein the outer radius side of the curved staircase 10 is generally free-standing and is supported only at the upper and lower levels 16, 14.

As will be described in greater detail below, inner and outer reinforcing panels 58, 62 that are layered over the stacked step modules 36 provide structural rigidity and strength to the assembly such that the free-standing side of the curved staircase 72 can support its own weight as well as the weight of persons or objects that are placed on the curved staircase 10. An additional embodiment of the step module 76 may be constructed similar to that which is shown in FIG. 2 b for the entirely free-standing version 74 of the curved staircase 10 which will be described in greater detail below.

Although the step modules 36 may be preassembled and pre-manufactured using specialized tooling, the inner and outer reinforcing panels 58, 62 may likewise be pre-manufactured using similar specialized tooling. The treads 54 may also be manufactured as individual components away from the job site under controlled conditions in order to produce a precisely dimensioned component of the curved staircase 10. The step modules 36, treads 54 and inner and outer reinforcing panels 58, 62 and other components may be pre-manufactured and shipped directly from the factory to the job site for assembly.

Referring now to FIGS. 1 and 3 b, for the inside radius free-standing 72 version, shown is the building structure 12 with the curved staircase 10 installed therein. The building structure 12 may have a framing 24 system comprised of the vertical wall studs 26. As can be seen, the front risers 46 are connected to the vertical wall studs 26. It is contemplated that the vertical wall studs 26 are preferably spaced and oriented to be compatible with the joining of the front risers 46 thereto. However, it is further contemplated that additional blocking 28 may be installed such as to allow for attaching of the front risers 46 should the wall studs 26 be misaligned with the front risers 46.

Each one of the wall studs 26 preferably extends between the upper and lower level 16, 14 although the wall studs 26 may be erected in any orientation or location within the framing 24. The wall studs 26 may extend from the upper level 16 down to the lower level 14 and may be interconnected to the lower level 14 at a bottom plate 30 which may be mounted on the lower level 14 (e.g., floor). The bottom plate 30 may be shaped complementary to the curved staircase 10. More particularly, it is contemplated that the bottom plate 30 and, hence, the wall studs 26, may be oriented in a curved shape.

The inner radius of the curved staircase 10 may be either concentric or non-concentric with the outer radius of the curved staircase 10. For the concentric version of the curved staircase 10, it is contemplated that the center of curvature of the wall studs 26 collectively forms a radius that is coaxial with the center of curvature of the inner radius of the curved staircase 10. For the non-concentric version of the curved staircase 10, it is contemplated that the center of curvature of the outer radius is offset from the center of curvature for the inner radius. The wall studs 26 are preferably disposed at a spacing to coincide with the angular spacing of the stacked set of step modules 36.

As shown in FIG. 4, the upper level 16 of the building structure 12 may be fabricated of a series of horizontally-aligned floor joists 20. The floor joists 20 form a joist system 18 to which the curved staircase 10 leads. In this regard, the floor joists 20 may define a walkway 32 structure that may connect to the curved staircase 10. The joist system 18 preferably includes at least one load-bearing beam 70 to which the curved staircase 10 attaches and by which it is supported at the upper level 16. At least one of the front riser 46 and tread ledger 48 and the step module 36 may be abutted against the beam 70 and may be connected thereto with mechanical fasteners such as nails or screws. The side panel 38 may also be connected to the beam 70 as shown in FIG. 4.

For configurations where the upper level 16 of the building structure 12 is curved, the inner and outer reinforcing panels 58, 62 of the uppermost one of the step modules 36 may extend around the walkway 32 and may be connected to the joist system 18, as can be seen in FIG. 4. The walkway 32 may also include a facia sheet 34 mounted to a side thereof and which has a curved shape that is complementary to the curved shaped of the curved staircase 10. The walkway 32 may also be generally straight with the curved staircase 10 blending thereinto in a manner similar to that shown in FIG. 6 a.

Shown in FIG. 2 is the single-step version 76 of the step module 36 which is prefabricated. Each one of the single-step versions 76 of the step modules 36 is comprised of a side panel 38, a front riser 46 and a tread ledger 48 which extends outwardly from the side panel 38. The side panel 38 is also prefabricated and comprised of laminated members 40 and may be formed according to the disclosure in U.S. Pat. No. 4,955,168 issued to Barry, the entire contents of which is expressly incorporated by reference herein. The side panel 38 may be generally arcuately shaped (i.e., curved) with a radius of curvature and therefore has an outer convex surface 42 and an inner concave surface 44.

To achieve the particular radius of curvature, it is contemplated that the side panel 38 is formed of a plurality of the laminated members 40 that are layered over one another. As shown in the figures, the side panel 38 of the step module 36 may be comprised of six laminated members 40 that may be formed of bonded particulate material. The material from which the side panel 38 may be fabricated may be cellulose fiber, shredded paper, wooden particles, sawdust, and various combinations thereof.

The particulate material is bonded together via a matrix resin to form the laminate material. The individual ones of the laminated members 40 may consist of individual thin wooden members made of the particulate material and which are formed around a curved jig. The laminated members 40 may be bonded together in juxtaposition to one another so as to result in a unitary laminated structure 12 having a predetermined size and thickness. Under sufficient temperature, pressure and other conditions, the desired arcuate or circular shape may be formed into the laminated members 40 to result in the side panel 38. As described in U.S. Pat. No. 4,955,168, a mold may be used to form the side panel 38 in the desired radius of curvature. In this regard, the side panels 38 may be formed in any radius and at any length other than that shown in the figures and in any suitable manner including the process and materials disclosed in U.S. Pat. No. 4,955,168.

As shown in FIGS. 1-4, the side panels 38 of each one of the step modules 36 may include the laminated members 40 being formed of material that is ¼ inch thick in order to arrive at a total thickness of the side panel 38 of 1½ inches. However, any number of laminated members 40 of any thickness may be layered together. The side panel 38 thus forms a partial arch section that has an arc length sufficient for constructing the inner radius of the curved staircase 10.

Each one of the side panels 38 is preferably constructed at a riser height 50 which is preferably the height between each one of the vertical levels of the step modules 36. Local and/or national building codes generally prescribe the riser height 50. Extending from the outer convex surface 42 of the side panel 38 are the front riser 46 and tread ledger 48. As can be seen, the front riser 46 and tread ledger 48 are disposed in overlapping and abutting relationship to one another and are generally positioned on the outer convex surface 42 at an arc length that is compatible with a tread 54 depth. Similar to the riser height 50, the tread 54 depth may also be controlled by local and/or national building codes.

As can be seen by reference to FIGS. 1-4, the tread ledger 48 forms the aft mounting surface for the tread 54 while the front riser 46 forms the forward mounting surface for the tread 54 for the step module 36 immediately above. Therefore, the tread ledger 48 is formed at a riser height 50 that is generally equivalent to that of the side panel 38. More specifically, the side panel 38 and the tread ledger 48 may each have upper edges that are generally flush with one another such that the tread 54 may be supported by the tread ledger 48 upper edge, the front riser 46 upper edge and the side panel 38 upper edge. The tread ledger 48 generally abuts the outer surface convex of the side panel 38 and extends laterally therefrom.

The front riser 46 of each one of the step modules 36 may also have an upper edge which extends upwardly past the upper edges of the side panel 38 and tread ledger 48 to a level that is equal to that of the riser height 50. In this manner, the front riser 46 of each one of the step modules 36 determines the height of each one of the steps of the curved staircase 10. Therefore, the total height of each one of the front risers 46 is twice that of the side panels 38. More specifically, the side panel 38 and tread ledger 48 are preferably formed at a riser height 50 while the front riser 46 is formed at twice the riser height 50.

As can be seen by reference to FIGS. 1-4, the front riser 46 may include an inset portion wherein the upper portion of the front riser 46 extends over the upper edge of the side panel 38 and is generally flush with the inner concave surface 44 of the side panel 38. However, it is contemplated that the front riser 46 need not necessarily be flush with the side panel 38 but may be shaped in a variety of configurations. In order to facilitate the attachment of inner and outer reinforcement panels 58, 62 to the curved staircase 10, it is preferable that the end of the front riser 46 is generally flush with the inner concave surface 44 of the side panel 38.

The front riser 46 may be attached to the outer convex surface 42 of the side panel 38 and may have a lower portion that abuts the outer convex surface 42 in a manner similar to that described above for the attachment of the tread ledger 48 to the outer convex surface 42. It is contemplated that the front riser 46 and tread ledger 48 may be attached to the outer convex surface 42 of the side panel 38 by means of glues, adhesives and/or mechanical fasteners such as nails and/or screws. As was earlier mentioned, the front riser 46 and tread ledger 48 are preferably pre-assembled under controlled conditions at the factory and are then shipped to the job site. Materials from which the front riser 46 and tread ledger 48 may be fabricated include any suitable material such as wood and, more particularly, plywood and Versa-Lam which is commercially available from the Boise Cascade Corporation.

After the step modules 36 have been shipped to the job site, installation thereof is initiated by first connecting the front riser 46 and tread ledger 48 to one of the vertical wall studs 26 as shown in the figures. More specifically, the front riser 46 extends laterally from the side panel 38 and is connected to one of the wall studs 26 on the side thereof. The tread ledger 48 also extends laterally from the side panel 38 and is connectable to a front face of the wall stud 26. In certain framing 24 arrangements in the building structure 12 wherein an appropriate vertical wall stud 26 is not readily available adjacent to (i.e., is not aligned with) the front riser 46 and tread ledger 48, blocking 28 may be installed into the framing 24 wherein horizontal and/or vertical segments of wooden studs or other material may be framed in between the existing wall studs 26 to create an appropriate attach point that is aligned with the front riser 46 and tread ledger 48.

Each one of the step modules 36 is preferably disposed in stacked relationship to one another. In order to create steps for the curved staircase 10, the step modules 36 are disposed in angular spaced orientation with respect to one another. In this regard, the angular spacing and arcuate arrangement of the wall studs 26 is preferably compatible to that of the step modules 36 wherein the angular orientation and spacing between adjacent ones of the step modules 36 matches the angular spacing between the wall studs 26. A module joint 52 is formed between adjacent ones of the step modules 36.

The curved staircase 10 of the present invention further includes the plurality of treads 54 which are mounted on upper edges of the tread ledger 48 and side panel 38 of respective ones of the step modules 36 and the upper edge of the front riser 46 of the next lower (i.e., immediately adjacent) step module 36. The treads 54 may be tapered with the amount of taper in each one of the treads 54 being formed in relation to the angular orientation of adjacent ones of the front riser 46 and tread ledger 48 which extend from adjacent ones of the step modules 36. The width of the tread 54 is preferably measured from an inside concave surface of the outer reinforcing panels 62 to the wall studs 26. As can be seen in the figures, the step modules 36 are angularly spaced or oriented to create a suitable amount of tread 54.

Each one of the treads 54 is preferably mounted so as to be abutted up against the front riser 46 of the step module 36 upon which the tread 54 is mounted. Furthermore, the front riser 46 of the next lower adjacent step module 36 serves as the mounting surface for a forward portion of the tread 54. In order to provide the required nosing 56 that is typical of stair steps, the tread 54 may have an additional material portion (i.e., nosing 56) that extends slightly over each one of the front risers 46. However, it is contemplated that the nosing 56 may be altogether omitted. Alternatively, the nosing 56 may be extended over each one of the front risers 46 in any amount and may be provided with beveling along the edges thereof.

Regarding specific materials for the front riser 46 and tread ledger 48, any wooden or non-wooden material may be used. However, Versa-Lam and/or manufacturing grade plywood is preferred for the front riser 46 and tread ledger 48 due to its resistance to ill effects from moisture. In addition, manufacturing grade plywood is preferred over construction grade plywood and manufacturing grade plywood may retain its tolerances regardless of the amount of moisture absorbed thereinto. Resistance to moisture also insures a better fit of the curved staircase 10 when assembled into the building structure 12. Regarding materials from which the treads 54 may be fabricated, it is contemplated that any suitably hard and durable wooden or non-wooden material may be utilized. Examples of such materials include, but are not limited to, manufacturing grade plywood and/or any hard wood such as oak, mahogany, cherry, and birch.

It is contemplated that individual components including the treads 54 and the front riser 46 and tread ledger 48 may be fabricated using specialized tooling and or machinery and may further include the use of computer aided design (CAD) equipment which may be operatively coupled to such machinery in order to produce parts with a high degree of precision. As was earlier mentioned, such improved precision in dimensional tolerances of the individual components improves the degree to which the curved staircase 10 may be fitted to the building structure 12 in conformance with building codes.

Referring still to the figures, following the stacking and angular spacing of the individual ones of the step modules 36 from the upper level 16 down to the lower level 14 of the building structure 12, a plurality of the inner reinforcing panels 58 is then disposed in overlapping relationship to the inner concave surfaces 44 of the side panels 38 of adjacent ones of the step modules 36. Each one of the inner reinforcing panels 58 overlaps at least one of the module joints 52 to allow for interconnection of the step modules 36.

As shown in the figures, each one of the inner reinforcing panels 58 has generally horizontally disposed edges which abut against one another. A preferable configuration for each one of the inner reinforcing panels 58 is that they are sized to have a height that spans across at least one of the module joints 52. Furthermore, the inner reinforcing panels 58 may abut one another to form a plurality of inner panel joints 60 which are likewise formed in a horizontal orientation and are preferably disposed in staggered relationship to the module joints 52. The inner reinforcing panels 58 provide an additional structural load-carrying member which transfers loads across adjacent ones of the step modules 36. More specifically, each one of the inner reinforcing panels 58 carries loads across at least one of the module joints 52.

A plurality of the outer reinforcing panels 62 are also disposed in overlapping relationship to the inner reinforcing panels 58 and preferably span one of the inner panel joints 60. More specifically, the outer reinforcing panels 62 provide a structural load-carrying mechanism by which loads are distributed across the inner panel joints 60. Similar to that described above for the inner reinforcing panels 58, the outer reinforcing panels 62 may also abut one another to form a plurality of outer panel joints 64 which are preferably disposed in staggered relationship to the inner panel joints 60 and module joints 52. As shown in the figures, each one of the outer reinforcing panels 62 straddles one of the inner panel joints 60.

Both of the reinforcing panels 58, 62 may be fabricated using the same method discussed above for fabricating the side panels 38 as disclosed in U.S. Pat. No. 4,955,168. Preferably, the inner reinforcing panels 58 have an outer convex surface 42 that is prefabricated to match an inner concave surface 44 of the side panels 38. Likewise, the outer reinforcing panels 62 have an outer convex surface 42 that is prefabricated to match the inner concave surface 44 of the inner reinforcing panels 58.

Furthermore, the outer reinforcing panels 62 have an inner concave surface 44 to which a finished material such as drywall, finished wood or other coverings may be applied. The above-described configuration (i.e., shape, material, attachment arrangement) for the side panels 38 and inner and outer reinforcing panels 58, 62 is applicable for all configurations of the step modules 36 (i.e., the single-step version 76 as well as the dual-step version 78) and also is applicable to all configurations of the curved staircase 10 (i.e., the outside radius free-standing version, the inside radius free-standing 72 version as well as the entirely free-standing version 74).

An additional structural element may be installed at strategic locations on the curved staircase 10 in order to tie the curved staircase 10 into the building structure 12. More specifically, a strap member 22 may be applied to connect the curved staircase 10 to the upper level 16. As was earlier mentioned, the upper level 16 may include the joist system 18 comprising a plurality of horizontal floor joists 20. The strap member 22 may connect an uppermost one of the step modules 36 to the beam 70 which may be generally of larger size than the floor joists 20 of the joist system 18.

As shown in the figures, the strap member 22 is attached to the outer reinforcing panel 62 adjacent to the uppermost one of the step modules 36. The strap member 22 may be horizontally oriented as it attaches to the outer reinforcing panel 62 and then wraps around a lower edge of the side panel 38 and extends upwardly along the outer concave surface of the side panel 38 and interconnects to the beam 70 located at the upper level 16 of the building structure 12.

The strap member 22 is preferably fabricated of metallic material but may be formed of any material including non-metallic material. The strap member 22 may include a row of apertures or holes through which mechanical fasteners such as nails or drywall screws may be extended into the outer reinforcing panel 62, inner reinforcing panel 58 and ultimately into the side panel 38. At the beam 70, mechanical fasteners such as screws and/or nails may likewise be driven through the apertures and into the beam 70 to firmly attach the curved staircase 10 to the upper level 16 of the building structure 12.

Likewise, at the lower level 14, the strap member 22 may be further provided for anchoring the curved staircase 10 to the building structure 12. In a similar manner to that described above for the upper level 16, the strap member 22 may be attached to a lowermost one of the step modules 36 immediately adjacent to the lower level 14 and may extend laterally along the lower level 14. The strap member 22 may likewise be a metallic member with a row of perforations or holes formed therealong through which mechanical fasteners may be extended.

Nails or screws may be driven through the outer reinforcing panel 62, inner reinforcing panel 58 and into the side panel 38 of the step module 36. As can be seen, the strap member 22 may be generally vertically oriented where it attaches to the lowermost one of the step modules 36 and may then bend at a ninety degree angle and extend laterally along the lower level 14 or it may be attached thereto by use of mechanical fasteners such as screws or nails. It should be noted that the strap member 22 may be arranged to connect the lower level 14 to the curved staircase 10 in any manner.

Regarding materials from which the inner and outer reinforcing panels 58, 62 may be fabricated, it is contemplated that particle board may be utilized. The material may be pre-cut to a desired width and/or length that is complementary to the particular riser height 50 utilized in the curved staircase 10. Individual ones of the inner and outer reinforcing panels 58, 62 may be disposed in abutting edge-to-edge contact with one another when overlaid upon the side panels 38. The inner and outer reinforcing panels 58, 62 may have a length that is intentionally longer than that which is required for the finalized version of the curved staircase 10.

In this manner, following completion of installation of the curved staircase 10, the extra length of the inner and outer reinforcing panels 58, 62 may be trimmed or cut off at an angle that matches the rake or angle of the curved staircase 10 as it extends from the lower level 14 to the upper level 16. For example, as shown in FIG. 5, the inner and outer reinforcing panels 58, 62 may be trimmed off along the trim line (shown in dashed lines in FIG. 5) after assembly of the step modules 36.

Referring to FIG. 1, during construction of the curved staircase 10 and prior to pre-manufacturing of the individual-step modules 36, it is contemplated that markings regarding the curvature of the side panels 38 as well as the curvature or radius of the vertical wall studs 26 may be directly applied to the lower level 14 as a template by which the curved staircase 10 may be measured and installed. More specifically, the desired locations of each one of the step modules 36 may be applied as a radially extending line denoting the front edge of each one of the treads 54. In this manner, measurements of the radius of curvature 66 and tread 54 width may be recorded and used to pre-manufacture the individual components that make up the curved staircase 10 and individual ones of the step modules 36.

Furthermore, such radial markings allow for alignment and positioning of individual ones of the vertical wall studs 26 such that the wall studs 26 are generally in alignment with the front riser 46 and tread ledger 48 during installation of the curved staircase 10. As shown in FIGS. 1 and 6, markings of the radii of curvature 66 of the inner concave surfaces 44 of the side panel 38, the radii of curvature 67 of the inner reinforcing panels 58, and the radii of curvature 68 of the outer reinforcing panels 62 may be directly applied to the lower level 14 in order to provide a template or guide by which the curved staircase 10 may be installed.

In accordance with the markings of construction lines and arcs for the curved staircase 10, the side panels 38 may be pre-manufactured off-site at a factory wherein individual laminated members 40 are joined to one another using the above-described manufacturing process disclosed in U.S. Pat. No. 4,955,168. Likewise, individual ones of the front riser 46 and tread ledger 48 as well as the treads 54 may be further fabricated out of appropriate materials as was earlier discussed in accordance with radii of curvature 66, 67, 68 and angular spacings of the individual ones of the step modules 36.

Following fabrication of the individual components, the front riser 46 and tread ledger 48 may be joined to one another in abutting contact with ends thereof being abutted up against the outer convex surface 42 of the side panel 38. Furthermore, the tread ledger 48 and side panel 38 upper edges are preferably disposed to be generally flush with one another with the upper edge of the front riser 46 being extended upwardly above the side panel 38 at an amount generally equal to twice the riser height 50. The front riser 46 and tread ledger 48 are then glued and/or screwed or nailed together and then may be nailed to the side panel 38. The front riser 46 and tread ledger 48 are preferably fabricated with a length that is sufficient to be complementary to the tread 54 width.

Once the individual step modules 36 are formed, the same are then installed at the building structure 12 in accordance with the markings wherein the individual-step modules 36 are stacked in one-at-a-time fashion with the front riser 46 and tread ledger 48 being connected via mechanical fasteners and/or adhesive to the adjacent one of the wall studs 26. Once a least two of the step modules 36 have been stacked, the inner reinforcing panels 58 may be successively applied in a manner wherein the inner reinforcing panel 58 straddles at least one of the module joints 52. Following application of the inner reinforcing panels 58 from the lower level 14 to the upper level 16, the outer layer of reinforcing panels is then applied wherein at least one of the inner panel joints 60 are covered and straddled by a respective one of the outer reinforcing panels 62.

The extra length of the inner and outer reinforcing panels 58, 62 may then be trimmed off on either side of the inner reinforcing panels 58 (i.e. along a front edge of the panels near the nosing 56 and along a rear edge of the panels). The strap members 22 are applied using adhesives and/or mechanical fasteners or other suitable means to interconnect the curved staircase 10 to the upper level 16 and to the lower level 14 in the manner described above. Following the basic construction of the curved staircase 10, additional operations may be completed to finish off the curved staircase 10 and/or building structure 12. More specifically, balusters and railings may be applied on the inside radius of the curved staircase 10.

Drywall, finished wood or other materials may be applied to the vertical wall studs 26 and other portions of the curved staircase 10. Likewise, drywall, finished wood or other materials may be applied underneath the curved staircase 10 as well as along the outer reinforcing panels 62. By constructing the step modules 36 and inner and outer reinforcing panels 58, 62 off-site in individual fashion using precision manufacturing techniques, a structurally strong and cost-effective curved staircase 10 may be installed in the building structure 12 using unskilled labor with minimal juggling of schedules with framers and/or other finishers.

Referring now to FIG. 6, shown is the curved staircase 10 in the entirely free-standing version 74 which extends from the lower 14 to the upper 16 level of the structure 12 without any intermediate supports such that the curved staircase 10 bears its own weight without the structural support of a wall on either the inner or outer radius of the curved staircase 10. The curved staircase 10 may be constructed using the step modules 36 in the single-step version 76 and/or the dual-step version 78. For the curved staircase 10 constructed using the single-step version 76 of the step modules 36, each of the step modules 36 includes a spaced pair of side panels 38 and a front riser and tread ledger 46, 48 that extends between the side panels 38 and interconnects the side panels 38.

As was earlier mentioned, such side panels 38 are preferably formed using the methodology described in U.S. Pat. No. 4,955,168. The step modules 36 are disposed in stacked, angularly spaced relationship to one another and define a plurality of module joints 52 when stacked. A plurality of treads are mounted on the side panels 38 and on the tread ledger 48 of a respective one of the step modules 36 as well as on the front riser 46 of the immediately lower adjacent one of the step modules 36. As can be seen in FIG. 6, each one of the treads 54 spans the distance between the side panels 38 and preferably extends from the inner concave surface 44 of the outer reinforcing panel 62 on each side of the curved staircase 10.

The inner reinforcing panels 58 are applied over the side panels in the same manner as was earlier described above wherein the inner reinforcing panels 58 are disposed in overlapping relationship to the side panels 38 of adjacent ones of the step modules 36 for interconnecting the step modules 36. The inner reinforcing panels 58 are generally horizontally oriented and have edges that are disposed preferably in abutting relationship to one another such that adjacent ones of the inner reinforcing panels 58 form a plurality of inner panel joints 60 that are disposed in preferably staggered relationship to the module joints 52.

Likewise, the outer reinforcing panels 62 are disposed in overlapping relationship to the inner reinforcing panels 58 for interconnecting adjacent ones thereof. The outer reinforcing panels 62 form a plurality of outer panel joints 64 that are disposed in staggered relationship to the inner panel joints 60. The inner and outer reinforcing panels 58, 62 are, like the side panels 38, formed using the methodology as disclosed in U.S. Pat. No. 4,955,168. In this regard, the side panels 38, inner reinforcing panels 58 and outer reinforcing panels 62 are prefabricated from a plurality of laminated members.

Each one of the side panels 38 may be arcuately shaped and has the outer convex surface 42 and inner convex surface 44 each defining a radius of curvature. The side panels 38 of each one of the step modules 36 may have non-concentric radii curvature wherein their radii of curvature are offset from one another. The side panels 38 and tread ledger 48 of each one of the step modules 36 are preferably formed at the riser height 50 similar to that which was described earlier for the step module 36 used in the inside radius free-standing version 72 of the curved staircase 10 which utilized the single-step version 76 step module. The front riser 46 has an upper edge that extends upwardly past the side panel 38 upper edge to a level equal to that of the riser height 50.

The curved staircase 10 may also be fabricated using step modules 78 of the dual-step version 78. In this regard, construction of the individual components and assembly of the curved staircase 10 into the building structure 12 is facilitated in much the same manner as was earlier described for the step modules 36 of the single-step version 76. More specifically, the curved staircase 10 which utilizes the dual-step version 78 comprises a plurality of step modules 36 each including a spaced pair of side panels 38 wherein each one of the side panels 38 has a main portion 82 with a front extension 80 protruding outwardly therefrom.

As shown in FIG. 5, the main portion 82 is constructed at a height which is twice that of the height of the front extension 80. The front extension 80 is preferably formed at the riser height 50 while the main portion 82 is preferably formed at twice the riser height 50. The step modules 36 of the dual-step version 78 also include a pair of riser assemblies extending between and interconnecting the spaced pair of side panels 38. Each of the riser assemblies may comprise a forward and an aft riser assembly 84, 86 which are disposed in spaced, staggered relationship to one another and which extend between the side panels 38.

Each of the individual ones of the riser assemblies comprise a front riser 46 and a tread ledger 48 which are preferably abutted up against one another. The front riser 46 extends upwardly past the tread ledger 48. The tread ledger 48 of the forward riser assembly 84 has an upper edge that is generally flush with the front extension 80 upper edge. The front riser 46 of the forward riser assembly 84 has an upper edge that is generally flush with the main portion 82 upper edge. The tread ledger 48 of the aft riser assembly 86 has an upper edge that is generally flush with the main portion 82 upper edge while the front riser 46 of the aft riser assembly 86 also has an upper edge that extends upwardly past the main portion 82 upper edge to a level equal to that of the riser height 50.

The step modules 36 are disposed in stacked, angularly spaced relationship to one another and define a plurality of module joints 52 therebetween. Treads 54 are provided with the step modules 36 with each one of the treads 54 being supported by the side panels 38 and by a pair of the front risers 46 and tread ledgers 48 that are immediately adjacent to one another. Inner and outer reinforcing panels 58, 62 are provided on both sides of the curved staircase 10 in a manner similar to that which was earlier described. The inner and outer reinforcing panels 58, 62 are constructed similar to the construction of the side panels 38 in that such components are prefabricated using a plurality of laminated members 40 that are formed at a predetermined radius of curvature 67, 68. It should be noted that the side panels 38 of each one of the step modules 36 may have non concentric radii of curvature although concentric radii of curvature is also contemplated.

The curved staircase 10 of the entirely free-standing version 74 which utilizes either the step module 36 of the single-step version 76 or the dual-step version 78 may be connected to the upper level by means of the strap member 22. The application and configuration of the strap member 22 is similar to that which was earlier described wherein a strap member 22 may be attached to an upper most one of the step modules 36 and is connected to at least one beam 70 of a joist system 18.

Likewise, at least one strap member 22 may be provided on at least one and preferably both sides of the entirely free-standing version 74 of the curved staircase 10 at the lower level 14 of the building structure 12. The materials, configuration, and construction methodology for the entirely free-standing version 74 of the curved staircase 10 is similar to that which was earlier disclosed for the inside radius free-standing version 72 of the curved staircase 10. For example, the front riser 46 and tread ledger 48 of the curved staircase 10 of the entirely free-standing version 74 may include plywood and/or Versa-Lam material while the tread 54 may be fabricated of plywood.

Referring back to FIG. 1, the curved staircase 10 may be constructed as either the outside radius free-standing version or as the inside radius free-standing version 72 using the step module 36 in the dual-step version 78. For such a configuration, the curved staircase 10 extends between upper and lower levels 16, 14 of the building structure 12 which has a plurality of the spaced vertical wall studs 26. The curved staircase 10 comprises the step modules 36 which each include the side panel 38 having the main portion 82 with the front extension 80 protruding outwardly therefrom. The pair of riser assemblies extend laterally outwardly from the side panels 38 and are connectable to the wall studs 26 of the building structure 12.

As was further mentioned, each of the riser assemblies comprises the forward and aft riser assembly 84, 86 which are disposed in staggered relationship to one another. As can be seen in FIG. 5, the dual-step version 78 of the step module 36 has an aft riser assembly 86 that is disposed at a higher level than that of the forward riser assembly 84. Each riser assembly comprises a tread ledger 48 and a front riser 46 which extends upwardly past the tread ledger 48. The treads 54 of the curved staircase 10 are applied in the same manner as was described above for the inside radius free-standing version 72 of the curved staircase 10 that utilizes the single-step version 76 of the step modules 36.

Likewise, the configuration including the material, shape and interconnection of the components of the curved staircase 10 is similar to that described above. For example, the side panels 38, inner reinforcing panels 58 and outer reinforcing panels 62 are preferably prefabricated of a plurality of laminated member 40. Likewise, the side panels 38 are preferably arcuately shaped as are the inner and outer reinforcing panels 58, 62. The relative heights of the front extension 80, main portion 82, front riser 46 and tread ledger 48 is also similar to that which was described earlier for the entirely free-standing version 74 of the curved staircase 10 utilizing the dual-step version 78 of the step modules 36.

Additional modifications and improvements of the present invention may also be apparent to those of ordinary skill in the art. Thus, the particular combination of parts described and illustrated herein is intended to represent only certain embodiments of the present invention, and is not intended to serve as limitations of alternative devices within the spirit and scope of the invention. 

1. A step module for a staircase, comprising: at least one side panel; a front riser and a tread ledger extending laterally outwardly from the side panel.
 2. The step module of claim 1 wherein the side panel is fabricated from a plurality of laminated members.
 3. The step module of claim 1 wherein the side panel is arcuately shaped.
 4. The step module of claim 1 wherein: the side panel and tread ledger is formed at a riser height and each having upper edges that are generally flush with one another; the front riser having an upper edge that extends upwardly past the side panel upper edge to a level equal to that of the riser height.
 5. The step module of claim 1 wherein the front riser and tread ledger are disposed in abutting relation to one another.
 6. The step module of claim 1 wherein at least one of the front riser and tread ledger is configured to be attachable to a building structure for supporting the staircase.
 7. The step module of claim 1 wherein the step module is configured to be arranged in stacked relationship to an adjacent one of the step modules.
 8. A staircase, comprising: a plurality of step modules each including: a spaced pair of side panels; and a front riser and a tread ledger extending between the side panels; wherein the step modules are disposed in stacked relationship to one another and defining a plurality of module joints therebetween; a plurality of treads mounted on the side panels and tread ledger of a respective one of the step modules and on the front riser of the immediately lower adjacent one of the step modules; a plurality of inner reinforcing panels disposed in overlapping relationship to the side panels of adjacent ones of the step modules for interconnection thereof and forming a plurality of inner panel joints disposed in staggered relationship to the module joints; and a plurality of outer reinforcing panels disposed in overlapping relationship to the inner reinforcing panels for interconnecting adjacent ones thereof and forming a plurality of outer panel joints disposed in staggered relationship to the inner panel joints.
 9. The curved staircase of claim 8 wherein at least one of the side panels, inner reinforcing panels and outer reinforcing panels are fabricated from a plurality of laminated members.
 10. The curved staircase of claim 8 wherein at least one of the side panels is arcuately shaped and having an outer convex surface and an inner concave surface and defining a radius of curvature.
 11. The curved staircase of claim 8 wherein the side panels of each one of the step modules comprises an inner side panel and an outer side panel having non-concentric radii of curvature.
 12. The curved staircase of claim 8 wherein: the side panels and tread ledger of each one of the step modules are formed at a riser height and having upper edges that are generally flush with one another; the front riser having an upper edge that extends upwardly past the side panel upper edge to a level equal to that of the riser height.
 13. A staircase, comprising: a plurality of step modules each including: a spaced pair of side panels, each one of the side panels having a main portion with a front extension protruding outwardly therefrom; and a pair of riser assemblies extending between the side panels, each of the riser assemblies comprising a forward and an aft riser assembly disposed in staggered relationship to one another, each of the riser assemblies comprising a tread ledger and a front riser extending upwardly past the tread ledger; wherein the step modules are disposed in stacked relationship to one another and defining a plurality of module joints therebetween; a plurality of treads, each one of the treads being supported by the side panels and by a front riser and a tread ledger; a plurality of inner reinforcing panels disposed in overlapping relationship to the side panels of adjacent ones of the step modules for interconnection thereof, adjacent ones of the inner reinforcing panels forming a plurality of inner panel joints disposed in staggered relationship to the module joints; and a plurality of outer reinforcing panels disposed in overlapping relationship to the inner reinforcing panels for interconnecting adjacent ones thereof, forming a plurality of outer panel joints disposed in staggered relationship to the inner panel joints.
 14. The curved staircase of claim 13 wherein at least one of the side panels, inner reinforcing panels and outer reinforcing panels is prefabricated of a plurality of laminated members.
 15. The curved staircase of claim 13 wherein at least one of the side panels is arcuately shaped and having an outer convex surface and an inner concave surface and defining a radius of curvature.
 16. The curved staircase of claim 15 wherein the side panels of at least one of the step modules comprises an inner side panel and an outer side panel having non-concentric radii of curvature.
 17. The curved staircase of claim 13 wherein the front riser and tread ledger are disposed in abutting relation to one another.
 18. The curved staircase of claim 13 wherein: the front extension being formed at a riser height; the main portion being formed at twice the riser height; the tread ledger of the forward riser assembly having an upper edge that is generally flush with the front extension upper edge; the front riser of the forward riser assembly having an upper edge that is generally flush with the main portion upper edge; the tread ledger of the aft riser assembly having an upper edge that is generally flush with the main portion upper edge; the front riser of the aft riser assembly having an upper edge that extends upwardly past the main portion upper edge to a level equal to that of the riser height.
 19. The curved staircase of claim 13 wherein at least one of the side panels is formed of bonded particulate material.
 20. The curved staircase of claim 13 wherein at least one of the front riser and tread ledger is fabricated of Versa-Lam material.
 21. The curved staircase of claim 13 wherein at least one of the treads is fabricated of plywood.
 22. A staircase extending between upper and lower levels of a building structure having a plurality of spaced vertical wall studs, the staircase comprising: a plurality of step modules each including: a side panel having a main portion with a front extension protruding outwardly therefrom; and a pair of riser assemblies extending laterally outwardly from the side panel and being connectable to the wall studs, each of the riser assemblies comprising a forward and an aft riser assembly disposed in staggered relationship to one another, each of the forward and aft riser assemblies comprising a tread ledger and a front riser extending upwardly past the tread ledger; wherein the step modules are disposed in stacked relationship to one another and defining a plurality of module joints therebetween; a plurality of treads being supported by the side panel and by a front riser and a tread ledger; a plurality of inner reinforcing panels disposed in overlapping relationship to the side panels of adjacent ones of the step modules for interconnection thereof, adjacent ones of the inner reinforcing panels forming a plurality of inner panel joints disposed in staggered relationship to the module joints; and a plurality of outer reinforcing panels disposed in overlapping relationship to the inner reinforcing panels for interconnecting adjacent ones thereof, adjacent ones of the outer reinforcing panels forming a plurality of outer panel joints disposed in staggered relationship to the inner panel joints.
 23. The curved staircase of claim 22 wherein: the front extension is formed at a riser height; the main portion being formed at twice the riser height; the tread ledger of the forward riser assembly having an upper edge that is generally flush with the front extension upper edge; the front riser of the forward riser assembly having an upper edge that is generally flush with the main portion upper edge; the tread ledger of the aft riser assembly having an upper edge that is generally flush with the main portion upper edge; the front riser of the aft riser assembly having an upper edge that extends upwardly past the main portion upper edge to a level equal to that of the riser height. 